Conventional media for reading or reading/writing memory data by using light include optical recording media such as compact disks and DVDs (Digital Versatile Discs).
As an example of these media, reference 100 in FIG. 4 represents an optical recording medium used as a DVD, comprising first and second substrates 111, 121, first and second reflective films 115, 125 and a resin layer 140.
First reflective film 115 is formed on a surface of first substrate 111, and resin layer 140 is provided in tight contact with the side of first reflective film 115 opposite to first substrate 111. Second reflective film 125 is provided in tight contact with the side of resin layer 140 opposite to first reflective film 115, and second substrate 121 is provided on the side of second reflective film 125 opposite to resin layer 140.
Generally, resin layer 140 consists of a cured product of a photopolymerizable resin such as epoxy acrylate, in which impure ions such as chlorine ion are liable to remain during its preparation process and any impure ions or water remaining in resin layer 140 may chemically degrade reflective films 115, 125 in tight contact with resin layer 140.
Especially, on reflective films consisting of a thin metal film based on silver, chemical degradation such as oxidation or sulfurization is liable to be caused and degraded reflective films 115, 125 discolor to no longer serve as reflective films.
In order to prevent such chemical degradation, JPA No. 126370/1999 describes a method for protecting reflective films from a resin layer by forming a protective film consisting of silicon dioxide or the like on the surfaces of the reflective films and bringing the resin layer into tight contact with the surface of the protective film.
However, such a protective film had the disadvantage that a more complex process is required for manufacturing an optical recording medium and high costs are incurred.
The present invention was made to overcome the disadvantages of the prior art described above with the purpose of providing a photopolymerizable resin composition suitable for a resin layer formed in tight contact with reflective films of optical recording media.